Add a missing break.

Patch by Tobias Güntner.

I tried to write a test, but the only difference is the Changed value that
gets returned. It can be tested with "opt -debug-pass=Executions -functionattrs,
but that doesn't seem worth it.

llvm-svn: 205121

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -1649,6 +1649,7 @@ bool FunctionAttrs::inferPrototypeAttributes(Function &F) {
     setDoesNotThrow(F);
     setDoesNotCapture(F, 1);
     setDoesNotCapture(F, 2);
+    break;
   default:
     // Didn't mark any attributes.
     return false;